Method for preparing silicone hydrogels

ABSTRACT

The present invention provides a method and a formulation for consistently producing a silicone hydrogel material having relatively high oxygen permeability, relatively high ion permeability, and low modulus, and contact lenses prepared from a formulation of the invention or made of a silicone hydrogel material of the invention.

This application claims the benefit under 35 U.S.C.§ 119 (e) of U.S.provisional application Ser. No. 60/750,195 filed Dec. 14, 2005.

The present invention is related to a method for preparing a siliconehydrogel material. In particular, the present invention is related to amethod and a formulation for consistently producing a silicone hydrogelmaterial having relatively high oxygen permeability, relatively high ionpermeability, and low modulus, and contact lenses prepared from aformulation of the invention or made of a silicone hydrogel material ofthe invention.

BACKGROUND OF THE INVENTION

In recent years, soft silicone hydrogel contact lenses, for example,Focus NIGHT & DAY™ and O2OPTIX™ (CIBA VISION), and PureVision™ (Bausch &Lomb) become more and more popular because of corneal health benefitsprovided by their high oxygen permeability and comfort. Currentlyavailable silicone Hydrogels contact lenses are typically producedaccording to full molding processes involving disposable molds and apolymerizable mixture including at least one hydrophilic monomer, atleast one silicone-containing monomer or macromer, and a solvent.However, no made-to-order (MTO) or customized silicone hydrogel contactlenses are commercially available.

MTO or customized contact lenses can match a patient's prescriptionand/or have a base curve desired by the patient. But, there are at leasttwo problems associated MTO or customized contact lenses. First, asilicone hydrogel material is generally soft and sticky. It can only belathed at low temperature and low temperature lathing can have arelatively high operation cost. Commonly-assigned copending U.S. patentapplication Ser. No. 11/148,104 disclosed methods for makingroom-temperature lathable silicone hydrogel materials.

The second problem is the difficulty to consistently produce aroom-temperature lathable silicone hydrogel material with desiredphysical and mechanical properties (e.g., oxygen permeability, ionpermeability, elastic modulus (modulus), elongation strength, etc.).Typically, a polymer rod is first produced and then lathed to produce aMTO or customized contact lens. A polymer rod is obtained by slowlypolymerizing a lens-forming material in long glass tubes under wellcontrolled conditions (e.g., temperatures). This type of process has anumber of disadvantages that are inherent to bulk polymerization. First,the polymerization is highly exothermic and reaction kinetics are highlytemperature dependent. Dissipation of heat and therefore maintaining auniform temperature in the polymerization is a challenge since there isno stirring or solvent present during the polymerization process.Control of temperature within polymerization tubes is furthercomplicated by increases in viscosity as conversion of monomerincreases. These effects can lead to uncontrolled polymerization (runaway reaction) and large temperature gradients within the polymerizationtube. A polymer produced during uncontrolled polymerization can havenon-homogenous composition, variability in the sequence of monomersand/or macromers in the polymer chain, and/or physical defects such ascracks and voids, resulting in low yield and high production cost. Assuch, polymerization of a lens-forming material in a tube generally isperformed very slowly at a relatively low temperature, e.g., at 45° C. Aslight increase in temperature, for example, an increase of about tendegrees, would result in formation of inhomogeneous material and defectssuch as cracks and voids and thereby decrease dramatically the yield ofpolymer rods suitable for making MTO contact lenses. Furthermore,variability in the sequence of monomers and/or macromers in the polymerchain or composition can result in variation in properties such asoxygen permeability (Dk), ion permeability (IP) and mechanical strength.

Therefore, there are needs for methods for consistently preparing asilicone hydrogel material with desired properties.

SUMMARY OF THE INVENTION

The present invention, in one aspect, provides a method of makingsilicone-hydrogel contact lenses by directly lathing a silicone hydrogelmaterial. The method of the invention comprises: obtaining apolymerizable fluid composition including a siloxane-containing macromerwith ethylenically unsaturated group(s), a free radical initiator, andan organo-nitroxide, wherein ratio of percentage by weight of theorganonitroxide to the radical initiator in the polymerizable fluidcomposition is selected to enable the polymerization fluid compositionto be cured at an elevated temperature to obtain a silicone hydrogelmaterial having a good quality; filling one or more tubes with thepolymerizable fluid composition; curing the polymerizable fluidcomposition at the elevated temperature in the tubes to form a polymerin a form of rod which is free of cracks and voids; stripping away thetubes from the polymer; and lathing the polymer to produce the contactlenses having an oxygen permeability of at least about 40 barres, amodulus of about 1.5 MPa or less, and a water content of at least about15% by weight when fully hydrated.

The present invention, in another aspect, provides a silicone hydrogelmaterial, which is obtained by copolymerizing, at an elevatedtemperature, a polymerizable fluid composition comprising (a) at leastone siloxane-containing macromer with ethylenically unsaturatedgroup(s), (b) a free radical initiator, and (c) an organonitroxide,wherein ratio of percentage by weight of the organonitroxide to theradical initiator in the polymerizable fluid composition is selected toenable the polymerization fluid composition to be cured at an elevatedtemperature to obtain the silicone hydrogel material having a goodquality, an oxygen permeability of at least about 40 barres and amodulus of about 1.5 MPa or less and a water content of at least about15% by weight when fully hydrated.

The present invention, in a further aspect, provides an ophthalmicdevice having a copolymer material which is obtained by copolymerizing,at an elevated temperature, a polymerizable fluid composition comprising(a) at least one siloxane-containing macromer with ethylenicallyunsaturated group(s), (b) a radical initiator, and (c) anorganonitroxide, wherein ratio of percentage by weight of theorganonitroxide to the radical initiator in the polymerizable fluidcomposition is selected to enable the polymerization fluid compositionto be cured at an elevated temperature to obtain the copolymer materialwhich is free of cracks and voids and has an oxygen permeability of atleast about 40 barres, a modulus of about 1.5 MPa or less, and a watercontent of at least about 15% by weight when fully hydrated and thesilicone hydrogel material.

The present invention, in still a further aspect, provides a method forcast-molding of contact lenses. The method of the invention comprises:obtaining a polymerizable fluid composition including one or morepolymerizable components, a free radical initiator, and anorganonitroxide, wherein the polymerizable components are selected fromthe group consisting of a vinylic monomer, a macromer having one or moreethylenically unsaturated groups, a prepolymer with ethylenicallyunsaturated groups, and mixtures thereof, wherein ratio of percentage byweight of the organonitroxide to the free radical initiator in thepolymerizable fluid composition is selected to enable the polymerizationfluid composition to be cured at an elevated temperature to obtain apolymer material having a good quality and a reduced polymerizationshrinkage; introducing the polymerizable fluid composition into a moldfor making a contact lens; and polymerizing the polymerizable fluidcomposition in the mold to form a contact lens.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Reference now will be made in detail to the embodiments of theinvention. It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the scope or spirit of the invention. Forinstance, features illustrated or described as part of one embodiment,can be used on another embodiment to yield a still further embodiment.Thus, it is intended that the present invention cover such modificationsand variations as common within the scope of the appended claims andtheir equivalents. Other objects, features and aspects of the presentinvention are disclosed in or are obvious from the following detaileddescription. It is to be understood by one of ordinary skill in the artthat the present discussion is a description of exemplary embodimentsonly, and is not intended as limiting the broader aspects of the presentinvention.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Generally, the nomenclatureused herein and the laboratory procedures are well known and commonlyemployed in the art. Conventional methods are used for these procedures,such as those provided in the art and various general references. Wherea term is provided in the singular, the inventors also contemplate theplural of that term. The nomenclature used herein and the laboratoryprocedures described below are those well known and commonly employed inthe art.

An “ophthalmic device”, as used herein, refers to a contact lens (hardor soft), an intraocular lens, a corneal onlay, other ophthalmic devices(e.g., stents, glaucoma shunt, or the like) used on or about the eye orocular vicinity.

“Contact Lens” refers to a structure that can be placed on or within awearer's eye. A contact lens can correct, improve, or alter a user'seyesight, but that need not be the case. A contact lens can be of anyappropriate material known in the art or later developed, and can be asoft lens, a hard lens, or a hybrid lens. Typically, a contact lens hasan anterior surface and an opposite posterior surface and acircumferential edge where the anterior and posterior surfaces aretapered off.

The “front or anterior surface” of a contact lens, as used herein,refers to the surface of the lens that faces away from the eye duringwear. The anterior surface, which is typically substantially convex, mayalso be referred to as the front curve of the lens.

The “rear or posterior surface” of a contact lens, as used herein,refers to the surface of the lens that faces towards the eye duringwear. The rear surface, which is typically substantially concave, mayalso be referred to as the base curve of the lens.

“Ocular environment”, as used herein, refers to ocular fluids (e.g.,tear fluid) and ocular tissue (e.g., the cornea) which may come intointimate contact with a contact lens used for vision correction, drugdelivery, wound healing, eye color modification, or other ophthalmicapplications.

A “hydrogel” refers to a polymeric material which can absorb at least 10percent by weight of water when it is fully hydrated. Generally, ahydrogel material is obtained by polymerization or copolymerization ofat least one hydrophilic monomer in the presence of or in the absence ofadditional monomers and/or macromers.

A “silicone hydrogel” refers to a hydrogel obtained by copolymerizationof a polymerizable composition comprising at least onesilicone-containing vinylic monomer or at least one silicone-containingmacromer.

“Hydrophilic,” as used herein, describes a material or portion thereofthat will more readily associate with water than with lipids.

As used herein, “actinically” in reference to curing or polymerizing ofa polymerizable composition or material means that the curing (e.g.,crosslinked and/or polymerized) is performed by actinic irradiation,such as, for example, UV irradiation, ionized radiation (e.g. gamma rayor X-ray irradiation), microwave irradiation, and the like. Thermalcuring or actinic curing methods are well-known to a person skilled inthe art.

A “prepolymer” refers to a starting polymer which can be cured (e.g.,crosslinked and/or polymerized) actinically or thermally or chemicallyto obtain a crosslinked and/or polymerized polymer having a molecularweight much higher than the starting polymer. A “crosslinkableprepolymer” refers to a starting polymer which can be crosslinked uponactinic radiation to obtain a crosslinked polymer having a molecularweight much higher than the starting polymer.

A “monomer” means a low molecular weight compound that can bepolymerized. Low molecular weight typically means average molecularweights less than 700 Daltons.

A “vinylic monomer”, as used herein, refers to a low molecular weightcompound that has an ethylenically unsaturated group and can bepolymerized actinically or thermally. Low molecular weight typicallymeans average molecular weights less than 700 Daltons.

The term “olefinically unsaturated group” is employed herein in a broadsense and is intended to encompass any groups containing at leastone >C═C<group. Exemplary ethylenically unsaturated groups includewithout limitation acryloyl, methacryloyl, allyl, vinyl, styrenyl, orother C═C containing groups.

A “hydrophilic vinylic monomer”, as used herein, refers to a vinylicmonomer which is capable of forming a homopolymer that is water-solubleor can absorb at least 10 percent by weight water.

A “hydrophobic vinylic monomer”, as used herein, refers to a vinylicmonomer which is capable of forming a homopolymer that is insoluble inwater and can absorb less than 10 percent by weight water.

A “macromer” refers to a medium to high molecular weight compound orpolymer that contains functional groups capable of undergoing furtherpolymerizing/crosslinking reactions. Medium and high molecular weighttypically means average molecular weights greater than 700 Daltons.Preferably, a macromer contains ethylenically unsaturated groups and canbe polymerized actinically or thermally.

“Molecular weight” of a polymeric material (including monomeric ormacromeric materials), as used herein, refers to the number-averagemolecular weight unless otherwise specifically noted or unless testingconditions indicate otherwise.

A “polymer” means a material formed by polymerizing/crosslinking one ormore monomers, macromers and/or oligomers.

A “photoinitiator” refers to a chemical that initiates radicalcrosslinking and/or polymerizing reaction by the use of light. Suitablephotoinitiators include, without limitation, benzoin methyl ether,diethoxyacetophenone, a benzoylphosphine oxide, 1-hydroxycyclohexylphenyl ketone, Darocure® types, and Irgacure® types, preferablyDarocure® 1173, and Irgacure® 2959.

A “thermal initiator” refers to a chemical that initiates radicalcrosslinking/polymerizing reaction by the use of heat energy. Examplesof suitable thermal intiators include, but ore not limited to,2,2′-azobis(2,4-dimethylpenanenitrile),2,2′-azobis(2methylpropanenitrile), 2,2′-azobis(2-methylbutanenitrile),peroxides such as benzoyle peroxide, and the like. Preferably, thethermal initator is azobisisobutyronitrile (AIBN).

“Visibility tinting” in reference to a lens means dying (or coloring) ofa lens to enable the user to easily locate a lens in a clear solutionwithin a lens storage, disinfecting or cleaning container. It is wellknown in the art that a dye and/or a pigment can be used in visibilitytinting a lens.

“Dye” means a substance that is soluble in a solvent and that is used toimpart color. Dyes are typically translucent and absorb but do notscatter light. Any suitable biocompatible dye can be used in the presentinvention.

A “Pigment” means a powdered substance that is suspended in a liquid inwhich it is insoluble. A pigment can be a fluorescent pigment,phosphorescent pigment, pearlescent pigment, or conventional pigment,While any suitable pigment may be employed, it is presently preferredthat the pigment be heat resistant, non-toxic and insoluble in aqueoussolutions.

The term “fluid” as used herein indicates that a material is capable offlowing like a liquid.

“Surface modification”, as used herein, means that an article has beentreated in a surface treatment process (or a surface modificationprocess), in which, by means of contact with a vapor of liquid, and/orby means of application of an energy source (1) a coating is applied tothe surface of an article, (2) chemical species are absorbed onto thesurface of an article, (3) the chemical nature (e.g., electrostaticcharge) of chemical groups on the surface of an article are altered, or(4) the surface properties of an article are otherwise modified.Exemplary surface treatment processes include, but are not limited to, asurface treatment by energy (e.g., a plasma, a static electrical charge,irradiation, or other energy source), chemical treatments, the graftingof hydrophilic monomers or macromers onto the surface treatmentprocesses are plasma processes, in which an ionized gas is applied tothe surface of an article, and LbL coating processes.

Plasma gases and processing conditions are described more fully in U.S.Pat. Nos. 4,312,575 and 4,632,844 and published U.S. Patent Application2002/0025389, which are incorporated herein by reference. The plasma gasis preferably a mixture of lower alkanes and nitrogen, oxygen or aninert gas.

“LbL coating”, as used herein, refers to a coating that is notcovalently attached to an article, preferably a medical device, and isobtained through a layer-by-layer (“LbL”) deposition of polyionic (orcharged) and/or non-charged materials on an article. An LbL coating canbe composed of one or more layers, preferably one or more bilayers.

The term “bilayer” is employed herein in a broad sense and is intendedto encompass: a coating structure formed on a medical device byalternatively applying, in no particular order, one layer of a firstpolyionic material (or charged material) and subsequently one layer of asecond polyionic material (or charged material) having charges oppositeof the charges of the first polyionic material (or the chargedmaterial); or a coating structure formed on a medical device byalternatively applying, in no particular order, one layer of a firstcharged polymeric material and one layer of a non-charged polymericmaterial or a second charged polymeric material. It should be understoodthat the layers of the first and second coating materials (describedabove) may be intertwined with each other in the bilayer.

Formation of an LbL coating on an ophthalmic device may be accomplishedin a number of ways, for example, as described in U.S. Pat. No.6,451,871 (herein incorporated by reference in its entirety) and U.S.patent application publication Nos. U.S. 2001-0045676 A1, U.S.2001-0048975 A1, and U.S. 2004-0067365 A1 (herein incorporated byreference in their entireties). One coating process embodiment involvessolely dip-coating and dip-rinsing steps. Another coating processembodiment involves solely spray-coating and spray-rinsing steps.However, a number of alternatives involve various combinations ofspray-and dip-coating and rinsing steps may be designed by a personhaving ordinary skill in the art.

An “antimicrobial agent”, as used herein, refers to a chemical that iscapable of decreasing or eliminating or inhibiting the growth ofmicroorganisms such as that term is known in the art.

“Antimicrobial metals” are metals whose ions have an antimicrobialeffect and which are biocompatible. Preferred antimicrobial metalsinclude Ag, Au, Pt, Pd, Ir, Sn, Cu, Sb, Bi and Zn, with Ag being mostpreferred.

“Antimicrobial metal-containing nanoparticles” refer to particles havinga size of less than 1 micrometer and containing at least oneantimicrobial metal present in one or more of its oxidation states.

“Antimicrobial metal nanoparticles” refer to particles which is madeessentially of an antimicrobial metal and have a size of less than 1micrometer. The antimicrobial metal in the antimicrobial metalnanoparticles can be present in one or more of its oxidation states. Forexample, silver-containing nanoparticles can contain silver in one ormore of its oxidation states, such as Ag⁰, Ag¹⁺, and Ag²⁺.

“Stabilized antimicrobial metal nanoparticles” refer to antimicrobialmetal nanoparticles which are stabilized by a stabilizer during theirpreparation. Stabilized antimicrobial metal nano-particles can be eitherpositively charged or negatively charged or neutral, largely dependingon a material (or so-called stabilizer) which is present in a solutionfor preparing the nano-particles and can stabilize the resultantnano-particles. A stabilizer can be any known suitable material.Exemplary stabilizers include, without limitation, positively chargedpolyionic materials, negatively charged polyionic materials, polymers,surfactants, salicylic acid, alcohols and the like.

The “oxygen transmissibility” of a lens, as used herein, is the rate atwhich oxygen will pass through a specific ophthalmic lens. Oxygentransmissibility, Dk/t, is conventionally expressed in units ofbarrers/mm, where t is the average thickness of the material [in unitsof mm] over the area being measured and “barrer/mm” is defined as:[(cm³oxygen)/(cm²)(sec)(mm²Hg)]×10⁻⁹

The intrinsic “oxygen permeability”, Dk, of a lens material does notdepend on lens thickness. Intrinsic oxygen permeability is the rate atwhich oxygen will pass through a material. Oxygen permeability isconventionally expressed in units of barrers, where “barrer” is definedas:[(cm³ oxygen)(mm)/(cm²)(sec)(mm² Hg)]×10⁻¹⁰These are the units commonly used in the art. Thus, in order to beconsistent with the use in the art, the unit “barrer” will have themeanings as defined above. For example, a lens having a Dk of 90 barrers(“oxygen permeability barrers”) and a thickness of 90 microns (0.090 mm)would have a Dk/t of 100 barrers/mm (oxygen transmissibilitybarrers/mm). In accordance with the invention, a high oxygenpermeability in reference to a material or a contact lens characterizedby apparent oxygen permeability of at least 40 barrers or largermeasured with a sample (film or lens) of 100 microns in thicknessaccording to a coulometric method described in Examples.

The “ion permeability” through a lens correlates with both the lonofluxDiffusion Coefficient and the lonoton Ion Permeability Coefficient.

The lonoflux Diffusion Coefficient, D, is determined by applying Fick'slaw as follows:D=−n′/(A×dc/dx)where

n′=rate of ion transport[mol/min]

A=area of lens exposed[mm²]

D=lonoflux Diffusion Coefficient[mm²/min]

dc=concentration difference[mol/L]

dx=thickness of lens[mm]

The lonoton Ion Permeability Coefficient, P, is then determined inaccordance with the following equation:In(1−2C(t)/C(0))=−2APt/Vdwhere:

C(t)=concentration of sodium ions at time t in the receiving cell

C(0)=initial concentration of sodium ions in donor cell

A=membrane area, i.e., lens area exposed to cells

V=volume of cell compartment (3.0 ml)

d=average lens thickness in the area exposed

P=permeability coefficient

An lonoflux Diffusion Coefficient, D, of greater than about 1.5×10⁻⁶mm²/min is preferred, while greater than about 2.6×10⁻⁶ mm²/min is morepreferred and greater than about 6.4×10⁻⁶ mm²/min is most preferred.

It is known that on-eye movement of the lens is required to ensure goodtear exchange, and ultimately, to ensure good corneal health. Ionpermeability is one of the predictors of on-eye movement, because thepermeability of ions is believed to be directly proportional to thepermeability of water.

The term “oxyperm component in a polymerizable composition” as usedherein, refers to monomers, oligomers, macromers, and the like, andmixtures thereof, which are capable of polymerizing with like or unlikepolymerizable materials to form a polymer which displays a relativelyhigh rate of oxygen diffusion there through.

The term “a reduced elastic modulus” is intended to describe that theelastic modulus of a silicone hydrogel material prepared from apolymerizable fluid composition with at least one chain transfer agentis lower than, preferably at least about 20%, more preferably at leastabout 30%, more preferably at least about 40% lower than that of acontrol silicone hydrogel material prepared from a control polymerizablecomposition, wherein the polymerizable fluid composition is prepared byadding the chain transfer agent into the control polymerizable fluidcomposition.

Room temperature (or ambient temperature) is defined as 22±6° C.

The term “lathability” in reference to a material is referred to itscapability to be machined into a contact lens with optical quality usingtypical lens lathing equipments. One gauge of lathability of a materialis its predominant glass transition temperature (T_(g)). Single phasepolymeric materials with one T_(g) below room temperature (i.e., lathingtemperature) are considered to be too soft for room temperature lathingwhereas those with T_(g) above room temperature (i.e., lathingtemperature), preferably at least 3 degrees above room temperature, havesufficient hardness for lathing at room temperature. Microscopicallymultiphasic polymeric materials may display one predominant (apparentlysingle) T_(g) or more than one T_(g). As long as a microscopicallymultiphasic polymeric material has a T_(g) (predominant glass transitiontemperature) associated with the dominant phase of the material being atroom temperature or above, it can be lathed into contact lenses at roomtemperature. “Dominant phase” is defined herein as a phase in amultiphasic material that determines the overall (bulk or working)hardness of a material.

The term “rod” refers to a cylinder cast-molded from a lens-formingmaterial in a tube, wherein the cylinder has a length of about 1 cm orlonger.

The term “button” refers to a short cylinder (with length of about 1 cmor less) cast-molded from a lens-forming material in a mold or directlycut out of a rod. In accordance with the present invention, both theopposite surfaces of a button can be flat and curved. For example, oneof the two opposite surfaces of a button can be a concave curved (e.g.,hemispherical) surface whereas the other surface is a convex curved(e.g., hemispherical) surface).

The term “bonnet” refers to a polymeric button cast-molded from alens-forming material in a mold, wherein at least one of the twoopposite surfaces of the bonnet has an optically finished surfacecorresponding to one of the anterior and posterior surfaces of a contactlens. The term “optically finished” in reference to a surface or a zonein a surface refers to a surface of a contact lens or a zone in asurface of a contact lens, wherein the surface or zone does not need toundergo further processing, e.g., such as, polishing or lathing. Onecould also machine lenses from pseudo bonnets. A pseudo bonnet is a partthat would require lathing of both sides of the material in order toobtain a contact lens. This type of part would allow for flexibility inthe design of the front and back surfaces of a lens while minimizingmaterial losses.

The term “polymerization shrinkage or volume change” as used herein isintended to describe a process in which the volume of a polymer materialobtained from polymerization of a polymerizable composition is smallerthan the volume of the polymerizable composition. Polymerizationshrinkage of a polymer material is preferably determined by firstpolymerizing a polymerizable composition in a glass tube (20 mm×300 mm),then determining the difference between the inner diameter of the tubeand the diameter of a resultant rod, and then calculating thepolymerization shrinkage$( \frac{{{Inner}\quad{Diameter}\quad{of}\quad{Tube}} - {{diameter}\quad{of}\quad{rod}}}{{Inner}\quad{diameter}\quad{of}\quad{tube}} ).$It is understood that other known polymerization shrinkage measurementscan also be used in the invention.

The term “a reduced polymerization shrinkage” is intended to describethat polymerization shrinkage of a polymer material prepared from apolymerizable fluid composition with a free radical initiator in thepresence of at least one organonitrioxide is smaller than that of acontrol polymer material prepared from a control polymerizablecomposition, wherein the polymerizable fluid composition is prepared byadding the chain transfer agent into the control polymerizable fluidcomposition.

The present invention is generally directed to methods for reliablyproducing a silicone hydrogel material, especially silicone hydrogelrods for making MTO contact lenses, with desired physical and mechanicalproperties. The present invention is partly based on the discovery thatby adding an organonitroxide to a polyrnerizable fluid composition (or alens-forming formulation or composition) in an amount to have a selectedratio of percentage by weight of the organonitroxide to the radicalinitiator in the polymerizable fluid composition, the polymerizationfluid composition can be cured in tubes at an elevated temperature toform rods which are substantially free of defects, such as, cracks andvoids) and have consistent properties (e.g., oxygen permeability, ionpermeability, water content, elastic modulus, and/or elongation). It isbelieved that an organonitroxide can mediate a free radicalpolymerization. By adjusting ratio of organonitrioxide to initiator, thepolymerization rate can be controlled to produce silicone hydrogel rodsof high quality (substantially free of structure defects, such as cracksand voids). Further, it is believed that organonitroxide mediatedpolymerization can be used to achieve better control of variability inthe sequence of monomers and/or macromers in the polymer chain,molecular weight, and polydispersity before gelation and for bettercontrol of branching and of molecular weight between cross-links. Theresultant materials are more homogeneous and have a more controllednetwork microstructure and consequently more consistent materialproperties. Material properties such as oxygen permeability, ionpermeability, and modulus play a critical role in corneal health andcomfort of contact lens users. These properties depend, in part, onpolymerization conditions and control of polymerization. By using suchmethod, one can produce silicone hydrogel rods with consistent desiredproperties, such as, high oxygen permeability, adequate water content,high ion permeability, low modulus, etc.

The invention is also related to an improved method for cast molding ofcontact lenses. It has been discovered that materials produced in thisinvention do not undergo significant shrinkage as evidenced by polymerrod having a very snug fit in glass tubes after curing and post curingoperations. As monomer is converted to polymer there is generally apolymerization shrinkage and the polymer (if in rod form) often pullsaway from the polymerization tube. Shrinkage during polymerization canlead to undesirable internal stress in the final part and poorreplication of mold surfaces. Therefore, the technologies described hereprovide a means of producing low strain materials and parts that havegood replication of molding surfaces. It is believed that low shrinkageobserved here might be that the high temperature curing. Hightemperature curing could result in a more amorphous less efficientlypacked structure. Low shrinkage and material homogeneity are importantfactors in the production of high quality precision moldings, such ascontact lenses.

The present invention, in one aspect, provides a method of makingsilicone-hydrogel contact lenses by directly lathing a silicone hydrogelmaterial. The method of the invention comprises: obtaining apolymerizable fluid composition including a siloxane-containing macromerwith ethylenically unsaturated group(s), a radical initiator, and anorganonitroxide, wherein ratio of percentage by weight of theorganonitroxide to the radical initiator in the polymerizable fluidcomposition is selected to enable the polymerization fluid compositionto be cured at an elevated temperature to obtain a silicone hydrogelmaterial having a good quality; filling one or more tubes with thepolymerizable fluid composition; curing the polymerizable fluidcomposition at the elevated temperature in the tubes to form a polymerin a form of rod which is free of cracks and voids; stripping away thetubes from the polymer; and lathing the polymer to produce the contactlenses having an oxygen permeability of at least about 40 barres, amodulus of about 1.5 MPa or less, and a water content of at least about15% by weight when fully hydrated.

A silicone hydrogel contact lens made according to a method of theinvention is characterized by having an oxygen permeability ofpreferably at least about 50 barres, more preferably about 60 barres,even more preferably about 70 barres and a modulus of preferably lessthan about 1.2 MPa, even more preferably less than about 1.0 MPa.

In accordance with the present invention, a polymerizable fluidcomposition can be a solution, a dispersion, a solvent-free liquid, or amelt at a temperature below 60° C.

Where a polymerizable fluid composition is a solution, it can beprepared by dissolving at least one siloxane-containing macromer withethylenically unsaturated group(s) and all other desired components inany suitable solvent known to a person skilled in the art. Examples ofsuitable solvents are alcohols, such as lower alkanols, for exampleethanol or methanol, and furthermore carboxylic acid amides, such asdimethylformamide, dipolar aprotic solvents, such as dimethyl sulfoxideor methyl ethyl ketone, ketones, for example acetone or cyclohexanone,hydrocarbons, for example toluene, ethers, for example THF,dimethoxyethane or dioxane, and halogenated hydrocarbons, for exampletrichloroethane, and also mixtures of suitable solvents, for examplemixtures of water with an alcohol, for example a water/ethanol or awater/methanol mixture.

Alternatively, a polymerizable fluid composition of the invention can beobtained by adding desired amounts of a radical initiator and anorganonitroxide into any formulations for making soft contact lenses.Exemplary formulations include without limitation the formulation oflotrafilcon A, lotrafilcon B, etafilcon A, genfilcon A, lenefilcon A,polymacon, acquafilcon A, and balafilcon.

Where a polymerizable fluid composition is a solvent-free liquid, it canbe prepared by dissolving at least one siloxane-containing macromer withethylenically unsaturated group(s) and all other desired components inan amount of one or more blending vinylic monomers. By removing solventfrom a polymerizable composition, an obtained silicone hydrogel materialmay not necessary to be subjected to a process in which a solvent isremoved from the silicone hydrogel material so as to reduce itsstickiness and/or softness and as such, the silicone hydrogel materialcan be directly lathed at room temperature to make contact lenses. Inaddition, it is discovered that by using a solvent-free polymerizablecomposition, one can obtain a silicone hydrogel material havingrelatively low level of extractable chemicals (i.e., so calledextractables). Therefore, a costly extraction process may not be neededin the production of contact lenses with a silicone hydrogel materialprepared from a solvent-free polymerizable composition.

In accordance with the invention, a “blending vinylic monomer” refers toa vinylic monomer which can function both as a solvent to dissolve bothhydrophilic and hydrophobic components of a polymerizable composition ofthe invention and as one of polymerizable components to be polymerizedto form a silicone hydrogel material. Preferably, the blending vinylicmonomer is present in the polymerizable composition in an amount of fromabout 5% to about 30% by weight.

Any suitable vinylic monomers, capable of dissolving both hydrophilicand hydrophobic components of a polymerizable composition of theinvention to form a solution, can be used in the invention. Preferredexamples of blending vinylic monomers include, without limitation,aromatic vinylic monomers, cycloalkyl-containing vinylic monomers. Thosepreferred blending monomers can increase the predominant glasstransition temperature of a silicone hydrogel material prepared bycuring a polymerizable composition containing those preferred blendingmonomer.

Examples of preferred aromatic vinylic monomers include styrene,2,4,6-trimethylstyrene (TMS), t-butyl styrene (TBS),2,3,4,5,6-pentafluorostyrene, benzylmethacrylate, divinylbenzene, and2-vinyinaphthalene. Of these monomers, a styrene-containing monomer ispreferred. A styrene-containing monomer is defined herein to be amonomer that contains a vinyl group bonded directly to a phenyl group inwhich the phenyl group can be substituted by other than a fused ring,e.g., as above with one to three C₁-C₆ alkyl groups. Styrene itself[H₂C═CH—C₆H₅] is a particularly preferred styrene-containing monomer.

A cycloalkyl-containing vinylic monomer is defined herein to be avinylic monomer containing a cycloalkyl which can be substituted by upto three C₁-C₆ alkyl groups. Preferred cycloalkyl-containing vinylicmonomers include, without limitation, acrylates and methacrylates eachcomprising a cyclopentyl or cyclohexyl or cycloheptyl, which can besubstituted by up to 3 C₁-C₆ alkyl groups. Examples of preferredcycloalkyl-containing vinylic monomers include isobornylmethacrylate,isobornylacrylate, cyclohexylmethacrylate, cyclohexylacrylate, and thelike.

In accordance with the present invention, one or more of acrylic acid,C₁-C₁₀ alkyl methacrylate (e.g., methylmethacrylate, ethylmethacrylate,propylmethacrylate, isopropylmethacrylate, t-butylmethacrylate,neopentyl methacrylate, methacrylonitrile, acrylonitrile, C₁-C₁₀ alkylacrylate, N-isopropyl acrylamide, 2-vinylpyridine, and 4-vinylpyridinecan be used as blending vinylic monomers. They can also be used togetherwith an aromatic vinylic monomer or a cycloalkyl-containing vinylicmonomer. Each of these blending vinylic monomer is capable of forming ahomopolymer with a glass transition temperature of above 30° C. As such,by using one or more of these blending monomers one can increase thepredominant glass transition temperature of a silicone hydrogel materialprepared by curing a polymerizable composition containing thosepreferred blending monomers.

In accordance with the present invention, any know suitablesiloxane-containing macromer with ethylenically unsaturated group(s) canbe used to produce a silicone hydrogel material. A particularlypreferred siloxane-containing macromer is selected from the groupconsisting of Macromer A, Macromer B, Macromer C, and Macromer Ddescribed in U.S. Pat No. 5,760,100, herein incorporated by reference inits entirety. Macromers that contain two or more polymerizable groups(vinylic groups) can also serve as cross linkers. Di and triblockmacromers consisting of polydimethylsiloxane and polyakyleneoxides couldalso be of utility. Such macromers could be mono or difunctionalizedwith acrylate, methacrylate or vinyl groups. For example one might usemethacrylate end cappedpolyethyleneoxide-block-polydimethylsiloxane-block-polyethyleneoxide toenhance oxygen permeability.

Radical initiators are materials well known for use in thepolymerization art to promote, and/or increase the rate of, thepolymerization reaction. In accordance with the invention, a radicalinitiator can be a photoinitiator or preferably a thermal initiator.

Suitable photoinitiators are benzoin methyl ether, diethoxyacetophenone,a benzoylphosphine oxide, 1-hydroxycyclohexyl phenyl ketone and Darocurand Irgacur types, preferably Darocur 1173® and Darocur 2959®. Examplesof benzoylphosphine initiators include2,4,6-trimethylbenzoyldiphenylophosphine oxide;bis-(2,6-dichlorobenzoyl)-4-N-propylphenylphosphine oxide; andbis-(2,6-dichlorobenzoyl)-4-N-butylphenylphosphine oxide. Reactivephotoinitiators which can be incorporated, for example, into a macromeror can be used as a special monomer are also suitable. Examples ofreactive photoinitiators are those disclosed in EP 632 329, hereinincorporated by reference in its entirety. The polymerization can thenbe triggered off by actinic radiation, for example light, in particularUV light of a suitable wavelength. The spectral requirements can becontrolled accordingly, if appropriate, by addition of suitablephotosensitizers.

Examples of suitable thermal initiators include, but are not limited to,2,2′-azobis(2,4-dimethylpentanenitrile),2,2′-azobis(2-methylpropanenitrile), 2,2′-azobis(2-methylbutanenitrile),azobisisobutyronitrile (AIBN), peroxides such as benzoyl peroxide, andthe like. Preferably, the thermal initiator is2,2′-azo-bis(2,4-dimethylvaleronitrile) (VAZO-52).

An organonitroxide is a compound having the formula of

in which R₁, and R₂ are independently H, an alkyl group, a cycloalkylgroup, an arenyl group, a heterocyclic group, or an aryl group; R₃ is analkyl group, a cycloalkyl group, an arenyl group, a heterocyclic group,or an aryl group; R₃ and R₂ or R₁ and R₂ may be joined together to forma cyclic ring structure that may have fused with it another saturated oraromatic ring; each of R₁, R₂, or R₃ may be substituted by at least onemember of the group consisting of hydroxyl group, sulfonate group,sulfate group, carboxylate group, amino group, ammonium group, alkoxygroup, aryloxy group, silyl group, boryl group, phosphino group, thiogroup, seleno group, and combinations thereof. Examples of preferredorganonitroxide includes without limitation2,2,6,6-tetramethylpiperidinoxy (TEMPO),4-oxo-2,2,6,6-tetramethyl-1-piperidine N-oxide (4-oxo-TEMPO),4-hydroxy-1-oxyl-2,2,6,6-tetramethylpiperidine (4-hydroxy-TEMPO).

In accordance with the invention, a polymerizable fluid compositioncomprises from about 0.05% to about 3%, preferably from about 0.1% toabout 2%, more preferably from about 0.2% to about 1.0%, even morepreferably from about 0.25% to about 0.7% by weight of a radicalinitiator.

In accordance with the invention, ratio of percentage by weight of theorganonitroxide to the radical initiator in the polymerizable fluidcomposition is from about 0.2 to about 1.5, preferably from about 0.3 toabout 1.1, even more preferably from about 0.4 to about 0.9. With aproper ratio of percentage by weight of the organonitroxide to theradical initiator in the polymerizable fluid composition, polymer rodscan be prepared by curing at an elevated temperature to have a goodquality (i.e., without substantial structure defects, such as cracks andvoids). The resultant polymer rods can further have more consistentproperties, such as, oxygen permeability, ion permeability, watercontent, modulus, elongation, or mixture thereof. In particular, oxygenpermeability and ion permeability of polymer rods can be enhanced.

Polymerization (curing) may be initiated by a number of well knowntechniques, which, depending on the polymerizable material, may includeapplication of radiation such as microwave, thermal, e-beam andultraviolet. A preferred method of initiating polymerization is byheating (i.e., thermal curing).

As used herein, the term “an elevated temperature” refers to atemperature of about 55° C. or above, preferably about 60° C. or above,more preferably about 70° C. or above, even more preferably about 80° C.or above.

The term “curing at an elevated temperature” as used herein is intendedto describe a process in which a polymerizable fluid composition issolidified, i.e., changing from liquid state to a solidified state(gel), at the elevated temperature. This term is not intended todescribe a post-curing process in which a gel is further solidified bypolymerizing residual polymerizable component in the gel.

In accordance with the present invention, a polymerizable fluidcomposition can also comprise siloxane-containing monomer. Any knownsuitable siloxane-containing monomers can be used in the presentinvention. Exemplary siloxane-containing monomers include, withoutlimitation, methacryloxyalkylsiloxanes, tristrimethylsilyloxysilylpropylmethacrylate (TRIS), 3-methacryloxy propylpentamethyldisiloxane andbis(methacryloxypropyl)-tetramethyldisiloxane. A preferredsiloxane-containing monomer is TRIS, which is referred to3-methacryloxypropyltris(trimethylsiloxy) silane, and represented by CASNo. 17096-07-0. The term “TRIS” also includes dimers of3-methacryloxypropyltris(trimethylsiloxy) silane.

In accordance with the present invention, a polymerizable fluidcomposition can also comprise a hydrophilic monomer. Nearly anyhydrophilic monomer that can act as a plasticizer can be used in thefluid composition of the invention. Suitable hydrophilic monomers are,without this being an exhaustive list, hydroxyl-substituted lower alkyl(C₁ to C₈) acrylates and methacrylates, acrylamide, methacrylamide,(lower allyl)acrylamides and -methacrylamides, ethoxylated acrylates andmethacrylates, hydroxyl-substituted (lower alkyl)acrylamides and-methacrylamides, hydroxyl-substituted lower alkyl vinyl ethers, sodiumvinylsulfonate, sodium styrenesulfonate,2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrole,N-vinyl-2-pyrrolidone, 2-vinyloxazoline,2-vinyl4,4′-dialkyloxazolin-5-one, 2- and 4-vinylpyridine, vinylicallyunsaturated carboxylic acids having a total of 3 to 5 carbon atoms,amino(lower alkyl)- (where the term “amino” also includes quaternaryammonium), mono(lower alkylamino)(lower alkyl) and di(loweralkylamino)(lower alkyl)acrylates and methacrylates, allyl alcohol andthe like.

Among the preferred hydrophilic monomers are N,N-dimethylacrylamide(DMA), 2-hydroxyethylmethacrylate (HEMA), hydroxyethyl acrylate,hydroxypropyl acrylate, hydroxypropyl methacrylate (HPMA),trimethylammonium 2-hydroxy propylmethacrylate hydrochloride,dimethylaminoethyl methacrylate (DMAEMA),dimethylaminoethyl-methacrylamide, acrylamide, methacrylamide, allylalcohol, vinylpyridine, glycerol methacrylate,N-(1,1dimethyl-3-oxobutyl)acrylamide, N-vinyl-2-pyrrolidone (NVP),acrylic acid, methacrylic acid, and N,N-dimethyacrylamide (DMA).

A polymerizable fluid composition can also comprise a hydrophobicmonomer. By incorporating a certain amount of hydrophobic monomer in apolymerizable fluid composition, the mechanical properties (e.g.,modulus of elasticity) of the resultant polymer may be improved.Examples of suitable hydrophobic vinylic comonomers includemethylacrylate, ethyl-acrylate, propylacrylate, isopropylacrylate,cyclohexylacrylate, 2-ethylhexylacrylate, methylmethacrylate,ethylmethacrylate, propylmethacrylate, vinyl acetate, vinyl propionate,vinyl butyrate, vinyl valerate, styrene, chloroprene, vinyl chloride,vinylidene chloride, acrylonitrile, 1-butene, butadiene,methacrylonitrile, vinyl toluene, vinyl ethyl ether,perfluorohexylethyl-thio-carbonyl-aminoethyl-methacrylate, isobornylmethacrylate, trifluoroethyl methacrylate, hexafluoro-isopropylmethacrylate, hexafluorobutyl methacrylate,tris-trimethylsilyloxy-silyl-propyl methacrylate,3-methacryloxypropyl-pentamethyl-disiloxane andbis(methacryloxypropyl)-tetramethyl-disiloxane. TRIS, which may act bothto increase oxygen permeability and to improve the modulus ofelasticity, is a particularly preferred hydrophobic monomer.

A polymerizable fluid composition can further comprise an antimicrobialagent, preferably antimicrobial metal nanoparticles, more preferablysilver nanoparticles.

A polymerization fluid composition can comprise a chain transfer agent.Any chain transfer agent can be used. Examples of preferred chaintransfer agent include without limitation mercaptans (e.g.,2-mercaptoethanol), alkane-thiols (e.g., ethanethiol, propanethiol,butanethiol), arylthiols (e.g., thiophenol), disulfide (e.g., di-n-butyldisulfide), carbon tetrabromide, carbon tetrachloride, chloroform,amines (e.g., ethylamine, diethlyamine, triethylamine, butylamine, diand tri-butylamine), methanol, ethanol, propanol, and isopropanol,acetic acid, and acetone. Preferably, a mercaptan is the chain transferagent.

In accordance with the present invention, a polymerizable fluidcomposition can further comprise various components, such ascross-linking agents, initiator, UV-absorbers, fillers, visibilitytinting agents (e.g., dyes, pigments, or mixtures thereof), and thelike.

Cross-linking agents may be used to improve structural integrity andmechanical strength. Examples of cross-linking agents include withoutlimitation allyl(meth)acrylate, lower alkylene glycol di(meth)acrylate,poly lower alkylene glycol di(meth)acrylate, lower alkylenedi(meth)acrylate, divinyl ether, divinyl sulfone, di- ortrivinylbenzene, trimethylolpropane tri(meth)acrylate, pentaerythritoltetra(meth)acrylate, bisphenol A di(meth)acrylate,methylenebis(meth)acrylamide, triallyl phthalate or diallyl phthalate. Apreferred cross-linking agent is ethylene glycol dimethacrylate (EGDMA).

The amount of a cross-linking agent used is expressed in the weightcontent with respect to the total polymer and is preferably in the rangefrom 0.05 to 5%, and more preferably in the range from 0.1 to 2%.Di-functional macromer (e.g. betacon) can be used as both a cross-linkerand a material to enhance Dk. In such cases this material will becomprise from about 20 to 46 weight percent of the total formulation.

In accordance with the present invention, the polymerizable fluidcomposition can further have one or more Tg-enhancing vinylic monomersselected from the group consisting of acrylic acid, C₁-C₄ alkylmethacrylate (e.g., methylmethacrylate, ethylmethacrylate,propylmethacrylate, isopropylmethacrylate, t-butylmethacrylate),methacrylonitrile, acrylonitrile, C₁-C₄ alkyl acrylate, N-isopropylacrylamide, 2-vinylpyridine, and 4-vinylpyridine. It is understood thataromatic monomers and/or cycloalkyl-containing vinylic monomers can bereplaced by one or more of the above Tg-enhancing vinylic monomers.

In a preferred embodiment, a polymerizable fluid composition suitablefor making an ophthalmic device will include (a) from about 20% to about46% by weight of a siloxane-containing macromer with ethylenicallyunsaturated group(s), (b) from about 5% to 30% by weight of asiloxane-containing monomer, (c) from about 10% to 35% by weight of ahydrophilic monomer, (d) from about 0.2% to about 1.0% by weight of aradical initiator, and (e) an amount of organonitrioxide sufficient tohave a ratio of percentage by weight of the organonitroxide to theradical initiator in the polymerizable fluid composition be from about0.3 to about 1.1. More preferably, the siloxane-containing monomer isTRIS.

In another preferred embodiment, a solvent-free polymerizablecomposition of the invention comprises: from about 20% to about 46% byweight of a siloxane-containing macromer with ethylenically unsaturatedgroup(s); from about 10% to about 30% by weight of a siloxane-containingvinylic monomer; from about 15% to about 50% by weight of a hydrophilicvinylic monomer; about 5% to about 20% by weight of a blending vinylicmonomer; from about 0.2% to about 1.0% by weight of a radical initiator;and an amount of an organonitrioxide sufficient to have a ratio ofpercentage by weight of the organonitroxide to the radical initiator inthe polymerizable fluid composition be from about 0.3 to about 1.1.

In another preferred embodiment, a polymerizable composition of theinvention comprises: from about 20% to about 46% by weight of asiloxane-containing macromer with ethylenically unsaturated group(s);from about 10% to about 30% by weight of a siloxane-containing vinylicmonomer; from about 15% to about 50% by weight of a hydrophilic vinylicmonomer; from about 5% to about 20% by weight of an aromatic vinylicmonomer, a cycloalkylmethacrylate or a cycloalkylacrylate; from about0.2% to about 1.0% by weight of a radical initiator; and an amount of anorganonitrioxide sufficient to have a ratio of percentage by weight ofthe organonitroxide to the radical initiator in the polymerizable fluidcomposition be from about 0.3 to about 1.1.

In another preferred embodiment, a polymerizable fluid compositionfurther comprises at least one antimicrobial agent, preferably silvernanoparticles in an amount sufficient to impart to the resultantsilicone hydrogel material an antimicrobial activity characterized byhaving at least a 5-fold reduction (≧80% inhibition), preferably atleast a 1-log reduction (≧90% inhibition), more preferably at least a2-log reduction (>99% inhibition), of viable microorganisms (e.g.,Pseudomonas aeruginosa GSU #3, or Staphylococcus aureus ATCC #6538),preferably by having a prolong antimicrobial activity (i.e., effectiveantimicrobial activity after direct contact with a body fluid over anextended period of time). Antimicrobial activity can be determinedaccording to procedure described in the Examples of U.S. patentapplication Ser. No. 10/891,407 filed on Jul. 14, 2004 (hereinincorporated by reference in its entirety).

As used herein, a “prolong antimicrobial activity” is characterized byhaving at least a 5-fold reduction (≧80% inhibition), preferably atleast a 1-log reduction (≧90% inhibition), more preferably at least a2-log reduction (≧99% inhibition), of viable microorganisms (e.g.,Pseudomonas aeruginosa GSU #3, or Staphylococcus aureus ATCC #6538)after at least 5, preferably at least 10, more preferably at least 20,even more preferably at least 30 consecutive soaking/rinsing cycles,each cycle comprising soaking/rinsing one lens in a phosphate bufferedsaline (PBS) for a period of time from about 24 to about 72 hours, asshown in the Examples of U.S. patent application Ser. No. 10/891,407filed on Jul. 14, 2004 (herein incorporated by reference in itsentirety).

The present invention, in another aspect, provides a silicone hydrogelmaterial, which is obtained by copolymerizing, at an elevatedtemperature, a polymerizable fluid composition comprising (a) at leastone siloxane-containing macromer with ethylenically unsaturatedgroup(s), (b) a radical initiator, and (c) an organonitroxide, whereinratio of percentage by weight of the organonitroxide to the radicalinitiator in the polymerizable fluid composition is selected to enablethe polymerization fluid composition to be cured at an elevatedtemperature to obtain the silicone hydrogel material having a goodquality, an oxygen permeability of at least about 40 barres and amodulus of about 1.5 MPa or less and a water content of at least about15% by weight when fully hydrated.

Any silicone or siloxane-containing vinylic monomers,siloxane-containing polymerizable macromers, organonitrioxide,hydrophilic vinylic monomers, blending vinylic monomers, Tg-enhancingvinylic monomers, aromatic vinylic monomers, cycloalkyl-containingvinylic monomers, cross-linking agents, hydrophobic vinylic monomers,free radical initiator, UV-absorbers, fillers, visibility tintingagents, antimicrobial agents, and polymerizing (curing) techniquesdescribed above can be used in this aspect of the invention.

A silicone hydrogel material of the invention has an oxygen permeabilityof preferably at least about 50 barrers, more preferably at least about65 barrers, even more preferably at least about 80 barrers. Inaccordance with the invention, an oxygen permeability is an apparent(directly measured when testing a sample with a thickness of about 100microns) oxygen permeability according to procedures described inExamples.

A silicone hydrogel material of the invention has a elastic modulus ofabout 1.5 MPa or less, preferably about 1.2 MPa or less, more preferablyabout 1.0 or less, even more preferably from about 0.4 MPa to about 1.0MPa.

A silicone hydrogel material of the invention has an lonoflux DiffusionCoefficient, D, of, preferably at least about 1.5×10⁻⁶ mm²/min, morepreferably at least about 2.6×10⁻⁶ mm²/min, even more preferably atleast about 6.4×10⁻⁶ mm²/min.

A silicone hydrogel material of the invention has a water content ofpreferably from about 18% to about 55%, more preferably from about 20%to about 38% by weight when fully hydrated. The water content of asilicone hydrogel material or a lens can be measured according to BulkTechnique as disclosed in U.S. Pat No. 5,849,811.

A silicone hydrogel material of the invention can find use in productionof ophthalmic devices, preferably contact lenses, more preferably MTO orcustomized contact lenses.

A silicone hydrogel material of the invention can further have apredominant glass-transition temperature of about 25° C. or higher,preferably about 30° C. or higher, more preferably about 35° C. orhigher, even more preferably about 45° C. or higher.

A silicone hydrogel material of the invention can further comprise atleast one antimicrobial agent, preferably silver nanoparticles in anamount sufficient to impart to the silicone hydrogel material anantimicrobial activity characterized by having at least a 5-foldreduction (≧80% inhibition), preferably at least a 1-log reduction (≧90%inhibition), more preferably at least a 2-log reduction (≧99%inhibition), of viable microorganisms (e.g., Pseudomonas aeruginosa GSU#3, or Staphylococcus aureus ATCC #6538), preferably by having a prolongantimicrobial activity (i.e., effective antimicrobial activity afterdirect contact with a body fluid over an extended period of time).Antimicrobial activity can be determined according to proceduredescribed in the Examples of U.S. patent application Ser. No. 10/891,407filed on Jul. 14, 2004 (herein incorporated by reference in itsentirety).

The present invention, in a further aspect, provides an ophthalmicdevice having a copolymer material which is obtained by copolymerizing,at an elevated temperature, a polymerizable fluid composition comprising(a) at least one siloxane-containing macromer with ethylenicallyunsaturated group(s), (b) a radical initiator, and (c) anorganonitroxide, wherein ratio of percentage by weight of theorganonitroxide to the radical initiator in the polymerizable fluidcomposition is selected to enable the polymerization fluid compositionto be cured at an elevated temperature to obtain the copolymer materialwhich is free of cracks and voids and has an oxygen permeability of atleast about 40 barres, a modulus of about 1.5 MPa or less, and a watercontent of at least about 15% by weight when fully hydrated and thesilicon hydrogel material.

Above described various embodiments and preferred embodiments of apolymerizable fluid composition and a method for making a siliconehydrogel material of the invention can be used in this aspect of theinvention.

An ophthalmic device of the invention preferably is a contact lens.

A contact lens of the invention has an oxygen permeability of preferablyat least about 50 barrers, more preferably at least about 65 barrers,even more preferably at least about 80 barrers. In accordance with theinvention, an oxygen permeability is an apparent (directly measured whentesting a sample with a thickness of about 100 microns) oxygenpermeability according to procedures described in Examples.

A contact lens of the invention has a elastic modulus of about 1.5 MPaor less, preferably about 1.2 MPa or less, more preferably about 1.0 orless, even more preferably from about 0.4 MPa to about 1.0 MPa.

A contact lens of the invention further has an lonoflux DiffusionCoefficient, D, of, preferably at least about 1.5×10⁻⁶ mm²/min, morepreferably at least about 2.6×10⁻⁶ mm²/min, even more preferably atleast about 6.4×10⁻⁶ mm²/min.

A contact lens of the invention further has a water content ofpreferably from about 18% to about 55%, more preferably from about 20%to about 38% by weight when fully hydrated. The water content of asilicone hydrogel contact lens can be measured according to BulkTechnique as disclosed in U.S. Pat. No. 5,849,811.

A contact lens of the invention further comprises at least oneantimicrobial agent, preferably silver nanoparticles in an amountsufficient to impart to the silicone hydrogel material an antimicrobialactivity characterized by having at least a 5-fold reduction (≧80%inhibition), preferably at least a 1-log reduction (≧90% inhibition),more preferably at least a 2-log reduction (≧99% inhibition), of viablemicroorganisms (e.g., Pseudomonas aeruginosa GSU #3, or Staphylococcusaureus ATCC #6538), preferably by having a prolong antimicrobialactivity (i.e., effective antimicrobial activity after direct contactwith a body fluid over an extended period of time). Antimicrobialactivity can be determined according to procedure described in theExamples of U.S. patent application Ser. No. 10/891,407 filed on Jul.14, 2004 (herein incorporated by reference in its entirety).

An ophthalmic device of the invention can be made according to any knownsuitable methods, such as, double-sided molding processes, cast-moldingprocesses, lathing, and combinations thereof.

Where an ophthalmic device of the invention is a contact lens, inparticular a MTO or customized contact lens, one can lathe directly atroom temperature a rod, preferably a button, more preferably a bonnet ofa silicone hydrogel material into the ophthalmic device. Any knownsuitable lathe apparatus can be used in this invention. Preferably, acomputer controllable (or numerically controlled) lathe is used in theinvention. More preferably, a numerically controlled two-axis lathe witha 45° piezo cutter or a lathe apparatus disclosed by Durazo and Morganin U.S. Pat. No. 6,122,999, herein incorporated by reference in itsentirety, is used in the invention. Exemplary preferred lathe apparatusinclude without limitation numerically controlled lathes from Precitech,Inc., for example, such as Optoform ultra-precision lathes (models 30,40, 50 and 80) having Variform piezo-ceramic fast tool servo attachment.A person skilled in the art will know how to prepare rods, buttons, andbonnets. For example, a rod can be produced preferably by thermallycuring a polymerizable composition of the invention in a tube made ofplastic or glass or quartz. The resultant rod optionally can besubjected to a post-curing treatment as described in the copending U.S.patent application, entitled “Method for Lathing Silicone HydrogelLenses”, herein incorporated by reference in its entirety. The diameterof a tube used in the preparation is larger than the diameter of thecontact lens. A rod can be further cut into buttons prior to lathing.However, it should be noted that it is possible for a tube diameter tobe smaller than a wet lens diameter. Lens formulations that containhydrophilic monomers usually have diameters which are larger in ahydrated state as compared to a dry state.

A person skilled in the art knows how to make molds for cast-molding orspin-casting polymer buttons. Preferably, a mold can be used to castmold buttons, the two opposite surfaces of each of which are curved. Forexample, one of the two opposite surfaces of a button can be a concavecurved (e.g., hemispherical) surface whereas the other surface is aconvex curved (e.g., hemispherical) surface. Advantage of cast-moldingbuttons with two opposite curved surfaces is that less silicone hydrogelmaterial is cut away and therefore wasted. The two curved surfaces of abutton can have identical or different curvatures. Preferably, the twocurved surfaces are spherical. One could also produce a button with oneflat surface and one curved surface.

Where a contact lens (e.g., toric or translating multifocal lens)requires orientation and/or translation features, it would beadvantageous that the entire posterior surface and a target geometry,common to all contact lenses and outside of the optical zone, of theanterior surface of a contact lens can be formed by curing apolymerizable composition in a mold for making a bonnet while lathing ofa bonnet could be reduced to the finish cuts defining any desiredoptical zone geometry of the anterior surface of a contact lens whiledirectly molding. As such, time, cost and material waste associated withthe production of customized or made-to-order (MTO) contact lenses canbe minimized. Customized or made-to-order (MTO) contact lenses can bemade to match exactly to any patient's prescription. Such method isdescribed in detail in the copending U.S. patent application entitled“Method for Lathing Silicone Hydrogel Lenses”, herein incorporated byreference in its entirety. A mold for making such bonnets includes afirst mold half having a first molding surface with optical quality anda second mold half having a second molding surface, wherein the secondmolding surface has a substantially-annular peripheral molding zone withoptical quality, wherein the first molding surface defines the posteriorsurface of the contact lens, wherein the peripheral molding zone definesthe one or more non-optical zones on the anterior surface of the contactlens. A bonnet prepared from such a mold has one optically finishedsurface corresponding to the posterior surface of the contact lens andone surface having an optically finished zone corresponding to the oneor more substantially annular non-optical zones surrounding the centraloptical zone of the contact lens. One only needs to lathe surface areas,surrounded by the optically-finished zone on the side opposite to theoptically-finished surface, of the bonnet, thereby obtaining the contactlens. It is understood that such lens can be made by two-side lathing.

In a preferred embodiment, an ophthalmic device of the invention has ahydrophilic surface obtained by using a surface modification process.The hydrophilic surface refers to a surface having an averaged contactangle of 85 degrees or less when the ophthalmic device is fullyhydrated. Preferably, the hydrophilic surface is a plasma coating or anLbL coating. Alternatively, a hydrophilic surface can be obtained byincorporating leachable (non-crosslinkable) hydrophilic polymer into thepolymerizable fluid composition for making rods or buttons or bonnets.

An “average contact angle” refers to a contact angle of water on asurface of a material (measured by Sessile Drop method), which isobtained by averaging measurements of at least 3 individual samples(e.g., contact lenses). Average contact angles (Sessile Drop) of contactlenses can be measured using a VCA 2500 XE contact angle measurementdevice from AST, Inc., located in Boston, Mass. This equipment iscapable of measuring advancing or receding contact angles or sessile(static) contact angles. The measurements are preferably performed onfully hydrated materials.

Contact angle is a general measure of the surface hydrophilicity of acontact lens or an article (e.g., the cavity surface of a container). Inparticular, a low contact angle (when the drop is hydrophilic, e.g.water) corresponds to more hydrophilic surface.

In a preferred embodiment, the antimicrobial ophthalmic device comprisesat least 10 ppm, preferably at least 25 ppm, more preferably at least 40ppm, even more preferably at least 60 ppm silver nanoparticlesdistributed therein.

The present invention, in still a further aspect, provides a method forcast-molding of contact lenses. The method of the invention comprises:obtaining a polymerizable fluid composition including one or morepolymerizable components, a free radical initiator, and anorganonitroxide, wherein the polymerizable components are selected fromthe group consisting of a vinylic monomer, a macromer having one or moreethylenically unsaturated groups, a prepolymer with ethylenicallyunsaturated groups, and mixtures thereof, wherein ratio of percentage byweight of the organonitroxide to the free radical initiator in thepolymerizable fluid composition is selected to enable the polymerizationfluid composition to be cured at an elevated temperature to obtain apolymer material having a good quality and a reduced polymerizationshrinkage; introducing the polymerizable fluid composition into a moldfor making a contact lens; and polymerizing the polymerizable fluidcomposition in the mold to form a polymer contact lens.

Preferably, this casting method is for making silicone hydrogel contactlenses. Above described various embodiments and preferred embodiments ofa polymerizable fluid composition and a method for making a siliconehydrogel material of the invention can be used in this aspect of theinvention.

Methods of forming mold sections for cast-molding a contact lens aregenerally well known to those of ordinary skill in the art. The processof the present invention is not limited to any particular method offorming a mold. In fact, any method of forming a mold can be used in thepresent invention. However, for illustrative purposes, the followingdiscussion has been provided as one embodiment of forming a contact lensmold.

In general, a mold comprises at least two mold sections (or portions) ormold halves, i.e. first and second mold halves. The first mold halfdefines a first optical surface and the second mold half defines asecond optical surface. The first and second mold halves are configuredto receive each other such that a contact lens forming cavity is formedbetween the first optical surface and the second optical surface. Thefirst and second mold halves can be formed through various techniques,such as injection molding. These half sections can later be joinedtogether such that a contact lens-forming cavity is formed therebetween.Thereafter, a contact lens can be formed within the contact lens-formingcavity using various processing techniques, such as ultraviolet curing.

Examples of suitable processes for forming the mold halves are disclosedin U.S. U.S. Pat. No. 4,444,711 to Schad; U.S. Pat. No. 4,460,534 toBoehm et al.; U.S. Pat. No. 5,843,346 to Morrill; and U.S. Pat. No.5,894,002 to Boneberger et al., which are also incorporated herein byreference.

Virtually all materials known in the art for making molds can be used tomake molds for making contact lenses. For example, polymeric materials,such as polyethylene, polypropylene, Topas, and PMMA can be used. Othermaterials that allow UV light transmission could be used, such as quartzglass.

Thermal curing or actinic curing methods can be used to curing apolymerizable composition in a mold to form an ophthalmic lens. Suchcuring methods are well-known to a person skilled in the art.

In accordance with the invention, ratio of percentage by weight of theorganonitroxide to the free radical initiator in the polymerizable fluidcomposition is selected to provide a polymerization shrinkage ofpreferably about 10% or less, more preferably about 7% or less, evenmore preferably about 5% or less, most preferably about 3% or less.

The previous disclosure will enable one having ordinary skill in the artto practice the invention. In order to better enable the reader tounderstand specific embodiments and the advantages thereof, reference tothe following examples is suggested.

EXAMPLE 1

Unless otherwise stated, all chemicals are used as received.Differential scan calorimetric (DSC) experiments are carried out inaluminum pans in a nitrogen atmosphere using a TA Instruments 2910 DSC.The instrument is calibrated with indium. Glass tubes used for makingrods of silicone hydrogel materials are silanized prior to use. Lensesare extracted with isopropanol (isopropyl alcohol) for at least 4 hoursand subjected plasma treatment according to procedures described inpublished U.S. patent application No. 2002/0025389 to obtain plasmacoatings. Oxygen and ion permeability measurements are carried outeither with lenses after extraction and plasma coating or with lenseswithout plasma coating. Non-plasma coated lenses are used for tensiletesting and water content measurements. Oxygen permeability isdetermined using polargraphic method.

Ion Permeability Measurements. The ion permeability of a lens ismeasured according to procedures described in U.S. Pat. No. 5,760,100(herein incorporated by reference in its entirety. The values of ionpermeability reported in the following examples are relative ionofluxdiffusion coefficients (D/D_(ref)) in reference to a lens material,Alsacon, as reference material. Alsacon has an ionoflux diffusioncoefficient of 0.314×10⁻³ mm²/minute.

EXAMPLE 2 Synthesis of Siloxane-containing Macromer with EthylenicallyUnsaturated Group(s)

51.5 g (50 mmol) of the perfluoropolyether Fomblin® ZDOL (from AusimontS.p.A, Milan) having a mean molecular weight of 1030 g/mol andcontaining 1.96 meq/g of hydroxyl groups according to end-grouptitration is introduced into a three-neck flask together with 50 mg ofdibutyltin dilaurate. The flask contents are evacuated to about 20 mbarwith stirring and subsequently decompressed with argon. This operationis repeated twice. 22.2 g (0.1 mol) of freshly distilled isophoronediisocyanate kept under argon are subsequently added in a counterstreamof argon. The temperature in the flask is kept below 30° C. by coolingwith a waterbath. After stirring overnight at room temperature, thereaction is complete. Isocyanate titration gives an NCO content of 1.40meq/g (theory: 1.35 meq/g).

202 g of the α,ω-hydroxypropyl-terminated polydimethylsiloxane KF-6001from Shin-Etsu having a mean molecular weight of 2000 g/mol (1.00 meq/gof hydroxyl groups according to titration) are introduced into a flask.The flask contents are evacuated to approx. 0.1 mbar and decompressedwith argon. This operation is repeated twice. The degassed siloxane isdissolved in 202 ml of freshly distilled toluene kept under argon, and100 mg of dibutyltin dilaurate (DBTDL) are added. After completehomogenization of the solution, all the perfluoropolyether reacted withisophorone diisocyanate (IPDI) is added under argon. After stirringovernight at room temperature, the reaction is complete. The solvent isstripped off under a high vacuum at room temperature. Microtitrationshows 0.36 meq/g of hydroxyl groups (theory 0.37 meq/g).

13.78 g (88.9 mmol) of 2-isocyanatoethyl methacrylate (IEM) are addedunder argon to 247 g of the α,σ-hydroxypropyl-terminatedpolysiloxane-perfluoropolyether-polysiloxane three-block copolymer (athree-block copolymer on stoichiometric average, but other block lengthsare also present). The mixture is stirred at room temperature for threedays. Microtitration then no longer shows any isocyanate groups(detection limit 0.01 meq/g). 0.34 meq/g of methacryl groups are found(theory 0.34 meq/g).

The macromer prepared in this way is completely colorless and clear. Itcan be stored in air at room temperature for several months in theabsence of light without any change in molecular weight.

EXAMPLE 3

This example illustrates the effectiveness of high temperature polymerrod production utilizing organonitroxide mediated polymerization.

DMA (192.04 grams), macromer (225.36 grams) prepared in Example 2, TRIS(120.36 grams), styrene (60.29 grams), a free radical initiator (AIBN)(1.5125 grams), and 2,2,6,6-tetramethylpiperidinoxy (0.9980 grams)(TEMPO) are mixed to prepare a solvent free formulation shown in Table 1for making room temperature lathable silicone hydrogel materials. Theabove-prepared formulations are sparged with nitrogen and then pouredinto silanized glass test tubes (about 75 ml of the formulation). Eachtube is capped with rubber septa and then underwent degassing cycles asfollows. Vacuum is applied to each tube filled with the formulation forseveral minutes and then pressure is equalized with nitrogen. Suchdegassing pressure equalization operation is repeated three times. TABLE1 Formulation No. Macromer* TRIS DMA Styrene AIBN TEMPO 1 37.52 20.0431.97 10.04 0.2518 0.1662*Prepared in Example 2.

Formulation 1 are thermally cured according to the following thermalcuring schedule: (a) at 50° C. for 21 hours (not gel) in an oil bath;(b) at 70° C. for 6 hours (not gel); (c) at 80° C. for 48 hours (gel).The gelled rods are allowed to cool to room temperature and then postcured in a forced air oven, The post curing is performed as follows: 50°C. for 6 hours, then at 75° C. for 6 hours, then finally at 105° C. for30 hours. One hour ramp times are utilized as temperature was increasedduring post cure operations. The oven is programmed to cool over 6 hoursfrom the final cure temperature of 105° C. No substantial cracks andvoids are observed in obtained rods.

Polymer cut from cured rod is tested for glass transition temperature(Tg) according to DSC analysis at a scan rate of 20° C./minute. T_(g) ofdry polymer is 53-58° C. at the first scan and 52-61° C. at the secondscan.

Lens Preparation

Button Generation Process: Polymerized Silicone Hydrogel rods areremoved from the glass tubes. After separating the polymer rods from theglass tubes, rods are grinded using a center less grinding machine plusits grinding oil, in order to remove any superficial rod deformity dueto its polymerization process and to assure the same rod diameter timeafter time.

Button Trimming Process: Grinded polymer rods are converted into buttonsusing button trimming lathes. Each Silicone Hydrogel rod is loaded intothe button trimming lathe collet mechanism and four (4) forming carbidetools form the button shape while the spindle rotates at 3000revolutions per minutes. Silicone Hydrogel buttons are then packed intoaluminum bags to avoid any pre-hydration. Button trimming process takesplace in an environment condition of up to about 35%, preferably about20% relative humidity (Rh) at about 72° F.

Mini File generation: The geometry to achieve the lens design isdescribed in a file called mini file. The mini file (.MNI) is ageometric description of the profile to be generated that allows complexgeometries to be described with comparatively small files and the timeto process these files is relatively small when compared with job files(.JFL). Mini files for silicone Hydrogel are created using Mini FileEngine software package. The mini files describe any surface in areasonable number of zones and is unique for each order.

Lens Lathing: Once the polymer button and mini files have beengenerated, OPTOFORM lathes (any one of Optoform 40, Optoform 50, andOptoform 80 with or without the Variform or Varimax third axisattachment) plus their off axis conic generators are used to perform theconcave or convex lens lathing. Lathing step take place in anenvironment of 20%±2% Rh with a temperature of 72±2° F. During lathingnatural or synthetic control waviness diamond tools are used. Machiningspeed of lens lathing goes form 2500-10,000 RPM with feed rates thatranges form 10-30 mm/min. During lathing process, a compress air at adew point of about −60° F. is used for blow off debris for a clean cut.Finished parts are inspected for compliance.

Non-plasma coated and sterilized lenses are tested for modulus andOxygen permeability. For tensile testing, strain rate of 12 mm/min,gauge length of 6.5 mm, strips (2.90 mm width, and 0.096 mm thickness)are used. All samples are submerged in a saline bath during tensiletesting. Lenses are autoclaved prior to testing. Oxygen permeability oflenses are determined according to the method disclosed by Nicolson etal. (U.S. Pat. No. 5,760,100) (herein incorporated by reference in itsentirety). A plurality of lenses are tested and averaged oxygen and ionpermeabilities are used in testing. The modulus of contact lenses isabout 0.91 MPa. The averaged oxygen permeability of lenses is about 66barres. The averaged ion permeability, relative ionoflux diffusioncoefficients (D/D_(ref)) in reference to a lens material (Alsacon), isabout 1.8.

EXAMPLE 4

This example illustrates that polymer rod quality depends on the ratioof TEMPO to AIBN in nitroxide mediated copolymerization.

Formulation number 2: DMA (319.05 grams), macromer (380.51 grams)prepared in Example 2, TRIS (200.15 grams), styrene (100.01 grams), afree radical initiator (AIBN) (2.5030 grams), and2,2,6,6-tetramethylpiperidinoxy (TEMPO) (0.5198 grams) are mixed toprepare solvent free formulation shown in Table 2 for making roomtemperature lathable silicone hydrogel materials. Formulations 3: DMA(316.45 grams), macromer (380.28 grams) prepared in Example 2, TRIS(200.13 grams), styrene (100.10 grams), a free radical initiator (AIBN)(2.4995 grams), and 2,2,6,6-tetramethylpiperidinoxy (TEMPO) (1.0936grams) are mixed to prepare solvent free formulation shown in Table 2for making room temperature lathable silicone hydrogel materials. Theabove-prepared formulations are sparged with nitrogen and then pouredinto silanized glass test tubes (about 75 ml of the formulation). Eachtube is capped with rubber septa and then underwent degassing cycles asfollows. Vacuum is applied to each tube filled with the formulation forseveral minutes and then pressure is equalized with nitrogen. Suchdegassing pressure equalization operation is repeated three times. TABLE2 Formulation No. Macromer* TRIS DMA Styrene AIBN TEMPO 2 37.95 19.9631.82 9.97 0.25 0.052 3 38.01 20.00 31.63 10.00 0.25 0.109*Prepared in Example 2.

Glass tubes are washed, dried and then coated with a 2 weight percentsolution of silanizing agent in 98% isopropanol as follows. Tubes arefilled with silanizing agent, drained, inverted, placed in a rack andthen placed in an oven heated to 125° C. for 24 hours. The silanizingagent used is SR80M methylsiloxane product available from GE silicones(Waterford, N.Y.).

An amount of a formulation is added into the tubes after the aboveteatment. For curing in nitrogen, samples are de-gassed and thenpressurized with nitrogen (until septa bulge) three times before beingplaced in the cure bath. For cases involving curing in air, the samplesare de-gassed and then pressure is equalized by bleeding air into thetubes (three cycles) prior to placing samples in the cure bath.

Samples are cured in an oil bath at 80° C. for 22 hours and then postcured in a forced air oven at 105° C. for 24 hours.

Polymer rod quality is found to depend on the ratio of TEMPO to AIBN.Rods obtained from formulation 2 with a lower ratio (about 0.21) ofTEMPO to AIBN have poor quality as judged by extent of cracks. However,polymer rods produced from formulation 3 with a higher ratio (about0.44) of TEMPO to AIBN have good quality (only a few minor cracks).

Polymer cut from cured rod is tested for glass transition temperature(T_(g)) according to DSC analysis at a scan rate of 20° C./minute. T_(g)of dry polymer is about 70° C. at the second scan.

EXAMPLE 5

This example illustrates the effect of TEMPO in the absence of AIBN andalso the effect of having a 1:1 ratio of AIBN and TEMPO in a siliconehydrogel formulation.

Formulation number 4: DMA (93.15 grams), macromer (113.01 grams)prepared in Example 2, TRIS (60.20 grams), styrene (30.18 grams), andTEMPO (0.4560 grams) are mixed to prepare solvent free formulationsshown in Table 7 for making room temperature lathable silicone hydrogelmaterials. Formulation number 5: DMA (93.51 grams), macromer (113.28grams) prepared in Example 2, TRIS (60.06 grams), styrene (30.21 grams)AIBN (0.4560 grams), and TEMPO (0.4560 grams) are mixed to preparesolvent free formulations shown in Table 7 for making room temperaturelathable silicone hydrogel materials. The above-prepared formulationsare sparged with nitrogen and then poured into silanized glass testtubes (about 75 ml of the formulation). Each tube is capped with rubbersepta and then underwent degassing cycles as follows. Vacuum is appliedto each tube filled with the formulation for several minutes and thenpressure is equalized with nitrogen. Such degassing pressureequalization operation is repeated three times. TABLE 3 Formulation No.Macromer* TRIS DMA Styrene AIBN TEMPO 4 38.05 20.27 31.36 10.16 0 0.1535 38.02 20.16 31.38 10.14 0.154 0.153*Prepared in Example 2.

The above-prepared formulation is thermally cured and post curedaccording to the following schedule: (a) at 30° C. for 24 hours in anoil bath; (b) at 45° C. for 17 hours in an oil bath; (c) at 55° C. for24 hours in an oil bath; (d) at 65° C. for 17 hours in an oil bath; (e)at 75° C. for 17 hours in an oil bath; (f) at 85° C. for 18 hours in anoil bath; (f) at 95° C. for 2 hours in an oil bath; (g) at 110° C. for 1hour in a preheated forced air oven; and (h) at 125° C. for 4 hours in aforced air oven. Samples are subjected to additional heating in a forcedair oven as follows: 50°C. for 6 hours, 75°C. for 6 hours, and 105° C.for 30 hours. 60 minute ramp rates are used in the cure oven to reacheach cure temperature. A 6 hour cool down ramp is used to cool samplesfrom 125° C. to 30° C. at the end of post curing.

EXAMPLE 6

This example illustrates the use of 4-hydroxy-TEMPO

Formulations 6: DMA (66.25 grams), macromer (76.50 grams) prepared inExample 2, TRIS (36.10 grams), styrene (21.07 grams), a free radicalinitiator (AIBN) (0.5145 grams), and 4-hydroxy-TEMPO (0.3027 grams) aremixed to prepare solvent free formulation shown in Table 4 for makingroom temperature lathable silicone hydrogel materials. Theabove-prepared formulations are sparged with nitrogen and then pouredinto silanized glass test tubes (about 75 ml of the formulation). Eachtube is capped with rubber septa and then underwent degassing cycles asfollows. Vacuum is applied to each tube filled with the formulation forseveral minutes and then pressure is equalized with nitrogen. Suchdegassing pressure equalization operation is repeated three times. Thetubes were placed in a forced air oven and heated at 90° C. for 24hours. Polymer rods gelled within this time, but showed extensivecracks. TABLE 4 Formulation Macro- 4-hydroxy- No. mer* TRIS DMA StyreneAIBN TEMPO 6 33.00 17.98 33.00 10.16 0.2563 0.1508

EXAMPLE 7

Formulations 7: DMA (126.16 grams), macromer (152.15 grams) prepared inExample 2, TRIS (80.43 grams), styrene (40.52 grams), a free radicalinitiator (AIBN) (0.1.092 grams), and 4-hydroxy-TEMPO (0.4159 grams) aremixed to prepare solvent free formulation shown in Table 4 for makingroom temperature lathable silicone hydrogel materials. Theabove-prepared formulation was sparged with nitrogen and then degassed.Formulation was poured into silanized glass test tubes (about 66 gramsof the formulation per tube). The tubes used in this experiment were 20mm×300 mm. Each tube is capped with rubber septa and then underwentdegassing cycles as follows. Vacuum is applied to each tube filled withthe formulation for several minutes and then pressure is equalized withnitrogen. Such degassing pressure equalization operation is repeatedthree times. The tubes were placed in a forced air oven and heated at80° C. for 24 hours (polymer gelled within 16 hours); 105° C. for 24hours; and 125° C. for 24 hours. Samples were allowed to cool from 105°C. to 30° C. over 6 hours. Some of the polymer rods showed some cracks,but more than ½ of the rod polymer was judged to be usable. If wasnoticed that minimal shrinkage occurred during polymerization asevidenced by the snug fittings of the polymer rods within the glasstubes at the end of cure. TABLE 5 Formulation Macro- 4-hydroxy- No. mer*TRIS DMA Styrene AIBN TEMPO 7 37.96 20.07 31.48 10.11 0.2725 0.1038

In the absence of AIBN, formulation 4 containing about 0.15% TEMPO doesnot gel even after heating at 125° C. Formulation 5 containing about 1:1ratio of TEMPO to AIBN is partly gelled after heating at about 85° C.and is converted to solid polymer. But, the obtained polymer is soft,presumably due to high level of non-converted monomer and due toinsufficient amount of free radical initiator present in theformulation.

Although various embodiments of the invention have been described usingspecific terms, devices, and methods, such description is forillustrative purposes only. The words used are words of descriptionrather than of limitation. It is to be understood that changes andvariations may be made by those skilled in the art without departingfrom the spirit or scope of the present invention, which is set forth inthe following claims. In addition, it should be understood that aspectsof the various embodiments may be interchanged either in whole or inpart. Therefore, the spirit and scope of the appended claims should notbe limited to the description of the preferred versions containedtherein.

1. A method for making silicone-hydrogel contact lenses, comprisingsteps of: obtaining a polymerizable fluid composition including asiloxane-containing macromer with ethylenically unsaturated group(s), aradical initiator, and an organonitroxide, wherein ratio of percentageby weight of the organonitroxide to the radical initiator in thepolymerizable fluid composition is selected to enable the polymerizationfluid composition to be cured at an elevated temperature to obtain asilicone hydrogel material having a good quality; filling one or moretubes with the polymerizable fluid composition; curing the polymerizablefluid composition at the elevated temperature in the tubes to form apolymer in a form of rod which is free of cracks and voids; strippingaway the tubes from the polymer; and lathing the polymer to produce thecontact lenses having an oxygen permeability of at least about 40barres, a modulus of about 1.5 MPa or less, and a water content of atleast about 15% by weight when fully hydrated.
 2. The method of claim 1,wherein the organonitrioxide is a compound having the formula of

in which R₁, and R₂ are independently H, an alkyl group, a cycloalkylgroup, an arenyl group, a heterocyclic group, or an aryl group; R₃ is analkyl group, a cycloalkyl group, an arenyl group, a heterocyclic group,or an aryl group; R₃ and R₂ or R₁ and R₂ may be joined together to forma cyclic ring structure that may have fused with it another saturated oraromatic ring; each of R₁, R₂, or R₃ may be substituted by at least onemember of the group consisting of hydroxyl group, sulfonate group,sulfate group, carboxylate group, amino group, ammonium group, alkoxygroup, aryloxy group, silyl group, boryl group, phosphino group, thiogroup, seleno group, and combinations thereof.
 3. The method of claim 2,wherein the elevated temperature is about 60° C. or above.
 4. The methodof claim 2, wherein the elevated temperature is about 70° C. or above.5. The method of claim 3, wherein the ratio of percentage by weight ofthe organonitroxide to the radical initiator in the polymerizable fluidcomposition is from about 0.3 to about 1.1.
 6. The method of claim 2,wherein the radical initiator is present in an amount of from about 0.1%to about 1% by weight.
 7. A silicone hydrogel ophthalmic device,comprising a silicone hydrogel material which is obtained bycopolymerizing, at an elevated temperature, a polymerizable fluidcomposition comprising (a) at least one siloxane-containing macromerwith ethylenically unsaturated group(s), (b) a radical initiator, and(c) an organonitroxide, wherein ratio of percentage by weight of theorganonitroxide to the radical initiator in the polymerizable fluidcomposition is selected to enable the polymerization fluid compositionto be cured at an elevated temperature to obtain the silicone hydrogelmaterial having a good quality, an oxygen permeability of at least about40 barres and a modulus of about 1.5 MPa or less and a water content ofat least about 15% by weight when fully hydrated, wherein theorganonitrioxide is a compound having the formula of

in which R₁, and R₂ are independently H, an alkyl group, a cycloalkylgroup, an arenyl group, a heterocyclic group, or an aryl group; R₃ is analkyl group, a cycloalkyl group, an arenyl group, a heterocyclic group,or an aryl group; R₃ and R₂ or R₁ and R₂ may be joined together to forma cyclic ring structure that may have fused with it another saturated oraromatic ring; each of R₁, R₂, or R₃ may be substituted by at least onemember of the group consisting of hydroxyl group, sulfonate group,sulfate group, carboxylate group, amino group, ammonium group, alkoxygroup, aryloxy group, silyl group, boryl group, phosphino group, thiogroup, seleno group, and combinations thereof.
 8. The silicone hydrogelophthalmic device of claim 7, which is a contact lens.
 9. The siliconehydrogel ophthalmic device of claim 7, wherein the ophthalmic device hasan oxygen permeability of at least about 50 barrers.
 10. The siliconehydrogel ophthalmic device of claim 9, wherein the ophthalmic device hasa elastic modulus of about 1.2 MPa or less.
 11. The silicone hydrogelophthalmic device of claim 10, wherein the polymerizable fluidcomposition further comprises one or more members selected from thegroup consisting of a hydrophilic vinylic monomer, an antimicrobialagent, a silicon-containing vinylic monomer, a blending vinylic monomer,a cross-linking agent, an UV-absorbers, a visibility tinting agent. 12.The silicone hydrogel ophthalmic device of claim 10, wherein thepolymerizable fluid composition is a solvent-free liquid comprising ablending vinylic monomer, wherein the blending vinylic monomer is anaromatic vinylic monomer, a cycloalkyl-containing vinylic monomer, aTg-enhancing vinylic monomer, or a mixture thereof, wherein theTg-enhancing vinylic monomer is selected from the group consisting ofacrylic acid, C₁-C₁₀ alkyl methacrylate, methacrylonitrile,acrylonitrile, C₁-C₁₀ alkyl acrylate, N-isopropyl acrylamide,2-vinylpyridine, and 4-vinylpyridine.
 13. The silicone hydrogelophthalmic device of claim 12, wherein the blending vinylic monomer isan aromatic vinylic monomer which is styrene, 2,4,6-trimethylstyrene(TMS), t-butyl styrene (TBS), 2,3,4,5,6-pentafluorostyrene,benzylmethacrylate, divinylbenzene, or 2-vinylnaphthalene.
 14. Thesilicone hydrogel ophthalmic device of claim 12, wherein the blendingvinylic monomer is a vinylic monomer containing a cyclopentyl,cyclohexyl or cycloheptyl, which can be substituted by up to 3 C₁-C₆alkyl groups.
 15. The silicone hydrogel ophthalmic device of claim 10,wherein the polymerizable fluid composition comprising a hydrophilicvinylic monomer which is N,N-dimethylacrylamide (DMA),2-hydroxyethylmethacrylate (HEMA), 2-hydroxyethyl acrylate (HEA),hydroxypropyl acrylate, hydroxypropyl methacrylate (HPMA),trimethylammonium 2-hydroxy propylmethacrylate hydrochloride,dimethylaminoethyl methacrylate (DMAEMA), glycerol methacrylate (GMA),N-vinyl-2-pyrrolidone (NVP), dimethylaminoethylmethacrylamide,acrylamide, methacrylamide, allyl alcohol, vinylpyridine,N-(1,1dimethyl-3-oxobutyl)acrylamide, acrylic acid, methacrylic acid, ora mixture thereof.
 16. The silicone hydrogel ophthalmic device of claim10, wherein the radical initiator is present in an amount of from about0.1% to about 1% by weight, wherein the ratio of percentage by weight ofthe organonitroxide to the radical initiator in the polymerizable fluidcomposition is from about 0.3 to about 1.1.
 17. The silicone hydrogelophthalmic device of claim 16, wherein the elevated temperature is about60° C. or above.
 18. The silicone hydrogel ophthalmic device of claim10, wherein the polymerizable fluid composition includes (a) from about20% to about 46% by weight of a siloxane-containing macromer withethylenically unsaturated group(s), (b) from about 5% to 30% by weightof a siloxane-containing monomer, (c) from about 10% to 35% by weight ofa hydrophilic monomer, (d) from about 0.2% to about 1.0% by weight of aradical initiator, and (e) an amount of organonitrioxide sufficient tohave a ratio of percentage by weight of the organonitroxide to theradical initiator in the polymerizable fluid composition be from about0.3 to about 1.1.
 19. The silicone hydrogel ophthalmic device of claim10, wherein the polymerization fluid composition is a solvent-freepolymerizable composition which comprises: from about 0 to about 46% byweight of a siloxane-containing macromer with ethylenically unsaturatedgroup(s); from about 10% to about 30% by weight of a siloxane-containingvinylic monomer; from about 15% to about 50% by weight of a hydrophilicvinylic monomer; about 5% to about 20% by weight of a blending vinylicmonomer; from about 0.2% to about 1.0% by weight of a radical initiator;and an amount of an organonitrioxide sufficient to have a ratio ofpercentage by weight of the organonitroxide to the radical initiator inthe polymerizable fluid composition be from about 0.3 to about 1.1. 20.The silicone hydrogel ophthalmic device of claim 19, wherein theblending vinylic monomer is an aromatic vinylic monomer, acycloalkylmethacrylate, a cycloalkylacrylate, or a mixture thereof. 21.The silicone hydrogel ophthalmic device of claim 10, wherein thepolymerizable fluid composition further comprises silver nanoparticlesin an amount sufficient to impart to the resultant silicone hydrogelmaterial an antimicrobial activity characterized by having at least a5-fold reduction (≧80% inhibition) of viable microorganisms (e.g.,Pseudomonas aeruginosa GSU #3, or Staphylococcus aureus ATCC #6538). 22.The silicone hydrogel ophthalmic device of claim 16, wherein thesilicone hydrogel material has a predominant glass-transitiontemperature of about 25° C. or higher.
 23. A silicone hydrogel material,which is obtained by copolymerizing, at an elevated temperature, apolymerizable fluid composition comprising (a) at least onesiloxane-containing macromer with ethylenically unsaturated group(s),(b) a radical initiator, and (c) an organonitroxide, wherein ratio ofpercentage by weight of the organonitroxide to the radical initiator inthe polymerizable fluid composition is selected to enable thepolymerization fluid composition to be cured at an elevated temperatureto obtain the silicone hydrogel material having a good quality, anoxygen permeability of at least about 40 barres and a modulus of about1.5 MPa or less and a water content of at least about 15% by weight whenfully hydrated, wherein the organonitrioxide is a compound having theformula of

in which R₁, and R₂ are independently H, an alkyl group, a cycloalkylgroup, an arenyl group, a heterocyclic group, or an aryl group; R₃ is analkyl group, a cycloalkyl group, an arenyl group, a heterocyclic group,or an aryl group; R₃ and R₂ or R₁ and R₂ may be joined together to forma cyclic ring structure that may have fused with it another saturated oraromatic ring; each of R₁, R₂, or R₃ may be substituted by at least onemember of the group consisting of hydroxyl group, sulfonate group,sulfate group, carboxylate group, amino group, ammonium group, alkoxygroup, aryloxy group, silyl group, boryl group, phosphino group, thiogroup, seleno group, and combinations thereof.
 24. A method forcast-molding of contact lenses. The method of the invention comprises:obtaining a polymerizable fluid composition including one or morepolymerizable components, a free radical initiator, and anorganonitroxide, wherein the polymerizable components are selected fromthe group consisting of a vinylic monomer, a macromer having one or moreethylenically unsaturated groups, a prepolymer with ethylenicallyunsaturated groups, and mixtures thereof, wherein ratio of percentage byweight of the organonitroxide to the free radical initiator in thepolymerizable fluid composition is selected to enable the polymerizationfluid composition to be cured at an elevated temperature to obtain apolymer material having a good quality and a reduced polymerizationshrinkage; introducing the polymerizable fluid composition into a moldfor making a contact lens; and polymerizing the polymerizable fluidcomposition in the mold to form a contact lens, wherein theorganonitrioxide is a compound having the formula of

in which R₁, and R₂ are independently H, an alkyl group, a cycloalkylgroup, an arenyl group, a heterocyclic group, or an aryl group; R₃ is analkyl group, a cycloalkyl group, an arenyl group, a heterocyclic group,or an aryl group; R₃ and R₂ or R₁ and R₂ may be joined together to forma cyclic ring structure that may have fused with it another saturated oraromatic ring; each of R₁, R₂, or R₃ may be substituted by at least onemember of the group consisting of hydroxyl group, sulfonate group,sulfate group, carboxylate group, amino group, ammonium group, alkoxygroup, aryloxy group, silyl group, boryl group, phosphino group, thiogroup, seleno group, and combinations thereof.
 25. The method of claim24, wherein the polymerizable fluid composition comprises at least onesiloxane-containing macromer with ethylenically unsaturated group(s) ora silicone-containing vinylic monomer or both, wherein the contact lenshas an oxygen permeability of at least about 40 barres, a modulus ofabout 1.5 MPa or less, and a water content of at least about 15% byweight when fully hydrated.